Investment composition



June 7 1927.

c. L. CORFMAN INVESTMENT COMPOSITION Filed Dec. so. 1925 Patented June 7, 1927.

UNITED STATES CLIFFORD L. CORFMAN, OF SPOKANE, WASHINGTON.

INVESTMENT COMPOSITION.

Application filed December 30-, 1925.

The present invention relates to an improved investment composition especially adapted for use in dentistry. The composition or material is used in molds for the 6 investment of wax patterns for inlays,

crowns, bridge work and similar dental appliances where heat is to be used for soldering and easting'gold and other metals after the mold has been prepared.

According to well known dental practice. after the wax impression is made, mounted upon its stem and attached to its base memher, the whole is invested in material within a mold and the base and stem and wax impression subsequently removed, after which the mold may be baked to eliminate moisture and prepare the mold for casting.

After casting the investment material is broken away, and the casting should be ready for use after polishing.

Plaster of Paris is the customary material utilized for investment purposes, and I am aware that it has been proposed to use compositions or compounds which include 5 other elements or ingredients'in the material.

With all such materials difficulty is encountered and imperfect patterns result from expansion and contraction of the investment material or mold. and consequently inaccuraoies and imperfections follow in the casting or soldering operations, necessitating tedious and expensive work on the appliance before it can be put into use.

I have found that by the use of magnesite in combination with the plaster of Paris in the approximate proportions of two to one furnishes an investment material from which the moisture may thoroughly and with rapidity be eliminated from the matrix or mold and the latter'is not subjected to perceptible contraction or expansion. thereby insuring accuracy in resting and soldering operations; smooth surfaces are provided on the mold to which the cast metal will not adhere and therefore imperfections or ir- Serial No. 78,384.

In order that the invention may readily be understood I have illustrated in the accompanying drawings a matrix or mold in which the investment material is made according to my invention.

Figure 1 is a sectional view of the matrix or mold showing the wax impression and stem with its base in the material.

Figure 2 is a view of the matrix ready for pouring or casting.

A well known type of cylindrical shell 1 00 is utilized and upon the base 2 the wax stem 3 is built for supporting the wax impression 4 secured in usual mariner. The investment material is indicated ias 5 and is placed in the shell in plastic condition as 05 usual. After the base 2 has been removed the wax stem and impression may be melted in usual manner and removed, after which the matrix is baked or otherwise dried and the molten metal, as gold is poured into the 7 opening 6. In forming the investment material T use. approximately one part of plaster of Paris and two parts of magncsite. The plaster of Paris is of course finely ground, and the magnesite is dead burned and finely pulverized. The magnesite, which is a soft white mineral forms a base for the plaster of Paris which readily compounds with the base in the presence of a sufficient quantity of moisture for the purpose. The plaster of Paris and magnesite are thoroughly intermingled and intimately mixed to form a plastic composition of the desired consistency for properly investing the wax impressjon as indicated in Figure 1. The plastic mixture is capable of being solidly compacted to closely invest. the core or wax memhers, and after the base has been removed and the material set, the matrix is baked or. otherwise dried to remove moisture leaving a solid and substantial mold for the reception of the molten metal poured into the openin 6.

VVhi e the mold is hard and solid, it may yet readily be broken away from the crown, bridge or other accessory of the dental art that is cast in the matrix and the material can be thoroughly removed from the accesuse comprising magnesite as abase and sory with convenience and facility leaving plaster of Paris.

only a slight touching up or polishing of 2. An investment composition comprising the crown in its finished or completed form. approximately two parts magnesite and one 5 Having thus fully described my invention, part plaster of Paris.

what I claim as new and desire to secure by In testimony whereof I atfix my signa- Letters Patentis ture.

1. An investmentcomposition for dental CLIFFORD L. CORFMAN. 

